A variety of different apparati for sequentially feeding discrete sheets of paper to a machine are known in the art. In addition to conventional manual feeding devices, apparati are known which semi-automatically feed paper to typewriters from a stacked supply such as illustrated in U.S. Pat. Nos. 4,067,566 and 4,222,557.
With the advent of automated office procedures with mini-computers performing word processing, computing and other functins, sophisticated paper feeders have been developed to conform with the requirements of existing impact printing equipment. These currently available paper feeders use photosensors to determine the position of paper in the print mechanism along with electric clutches and brakes to perform the necessary synchronizing function of placing print in the proper vertical positon on the paper. U.S. Pat. No. 4,326,815 is illustrative of such prior art.
Because of the expense of the electric components, some other paper feeders use elaborate mechanisms in cooperation with electronic controls to synchronize paper feeding. This is done by backing up the platen roller, and thus the paper drive gear, a certain number of steps in mechanically engaging or disengaging certain feed means according to the number of steps taken. In such devices, a page is printed and then fed out into a stacker after which the electronic logic is directed to reverse the platen roller a discrete number of steps and then to feed forward a discrete number of steps to position the next page in the proper vertical place. Although such apparatus has the advantage of being able to select among several paper bins, depending upon the number of backsteps, and all-mechanical interfacing, this type apparatus also has a disadvantage of requiring special software programming in either the word processing controller or the printer.
It is an object of this invention to provide a significantly simplified paper sheet feeder having the advantage of all-mechanical interfacing to a computer controlled typewriter or printer without requiring any special or customized software or hardware in either the printer or word processor to feed successive sheets at precisely the right time in synchronization with a controller of the word processor. A related object of this invention is to provide such a feeder with a minimum number of relatively inexpensive parts in an attactive compact unit particularly easy to install and operate and which is capable of reliable and extensive use under demanding conditions with minimum service requirements. In particular, it is a further object to provide such a feeder which has no electrical interface or power requirements but rather is provided a simplified mechanical interface to a driving gear on the printer platen shaft and has the capability of printing subscripts, superscripts and plotting while additionally permitting manual single sheet or envelope bypass and eliminating page to page accumulated error. A related aim of this invention is to provide such a feeder capable of being "backed up" without encountering mechanical lock-up problems.
Other objects will be in part obvious and in part pointed out in more detail hereinafter.